The present invention is a process for removing residual chloride from polysiloxane fluids. The process involves contacting a weakly-basic alkaline metal compound with a chloride containing polysiloxane fluid at a temperature of 100.degree. C. or less. In a preferred embodiment of the present invention, water is added along with the alkaline metal compound to facilitate removal of residual chloride. The treated polysiloxane fluid, reduced in residual chloride content, is filtered to remove solid alkaline metal compounds.
Residual chloride may occur in polysiloxane fluids in a variety of forms. For example the chloride may be present as ionic chloride, as an alkyl chloride, or as chloride bound to silicon. Sources of chloride may be the feed-stocks used to prepare the polysiloxanes, equipment contamination, and added chlorosilanes. The presence of chloride in polysiloxane fluids has been shown to be correlated with such detrimental processes as color changes, viscosity changes, and increased electrical conductivity. To avoid these detrimental processes it is often desirable to reduce residual chloride content of polysiloxanes. The reduction of residual chloride must be achieved without detrimental effect on the polysiloxane.
Welch et al., U.S. Pat. No. 3,278,266, issued Oct. 11, 1966, describes a process for the separation of hydrogen halides from hydrocarbon mixtures. Welch et al. teaches the use of a diacid base, for example magnesium, calcium, strontium, and barium in the form of their respective oxides or hydroxides. The diacid base is deposited on a porous support. The process is run by contacting at temperature above 100.degree. C. and less than 300.degree. C. a vaporized hydrogen mixture with the diacid base.
Williams et al., U.S. Pat. No. 4,721,824, issued Jan. 26, 1988, describes a process whereby extruded particles of magnesium oxide are used to remove chlorides from toluene feedstocks. The particles of magnesium oxide are mixed with an inert binder prior to extrusion. Removal of the organic chlorides was reported to take place at a temperature within the range of 177.degree. C. to about 454.degree. C.
Morehead et al., U.S. Pat. No. 4,732,996, issued March 22, 1988, described a process in which an alkoxysilane is contacted with an alkaline metal compound using superatmospheric pressure to achieve a treatment temperature of greater than 130.degree. C. It is taught that this process will remove ionic chloride species such as free hydrogen chloride and unreacted chlorosilanes as well as non-ionic species including organic chloride materials.
None of the cited reference teach that, at a temperature of 100.degree. C. or less, selected weakly-basic alkaline metal compounds can be used to reduce residual chloride in a polysiloxane fluid without detrimental effects on the polysiloxane polymer. Furthermore, none of the cited reference teach that the reduction of residual chloride in polysiloxane fluid can be facilitated by the addition of water to the process.